Modification of semiconductors such as silicon wafers is often implemented by ion implantation. Commonly, irradiation uniformity is achieved using time-varying electric fields in two dimensions to rapidly deflect the ion beam such that it scans in a raster pattern across the wafer surface. A pair of oppositely acting deflections for each dimension produces parallel scanning of the wafer. In this type of implanter the beam current and hence the rate at which wafers can be processed is severely limited by the space charge forces which are present in the region of the time-varying electric fields and which cause beam "blow-up".
In a common variation, a time-varying electric field is used to deflect the beam back and forth along one axis, while the wafer is mechanically reciprocated along an orthogonal axis. Again, in many cases, the beam current and wafer throughput is unduly limited by space charge forces. Furthermore, the mechanical motion of the wafer is relatively slow which limits wafer throughput when the total irradiation dose is low.
Time varying magnetic fields, which are used at high frequencies for electron scanning, have been suggested for scanning of beams of atomic and molecular ions. However, for the heavy ions frequently used in the processing of wafers, such as singly charged boron (B+), phosphorous (P+), arsenic (As+), and antimony (Sb+), the necessary scanner field energy is 10,000 to 100,000 times greater for magnetic deflection compared with electric deflection.
The techniques developed for rapid magnetic scanning of electrons which are less than 1/10,000 the mass of implantation ions, cannot be scaled to produce a structure suitable for an ion implanter. Hitherto, magnetic scanning techniques used in ion implanters have been limited to scan frequencies of just a few Hz, and again these structures are either not applicable or cannot be scaled to produce two dimensional raster scanning at rapid scan frequencies, i.e. above 100 Hz and up to 1,000 Hz and higher.